Because they are relatively cheap and easy to build.
Throughout most of its history, America has had to produce thousands of dwellings cheaply and quickly to house the tens (and at times hundereds) of thousands of new immigrants arriving each year.
Europe has had hundreds of years to slowly increase its housing stock, while America had to do it in a short amount of time.
Also, private home ownership remains the dream of almost every American, so wood frame homes allow those with less financial means to own a home.
The old pioneers started that way and we are changing to a lot of engineered products. Metal framing, concrete siding and vinyl's. Last a lot longer and bricks are so darned heavy and expensive to lay here. I visited Holland and they were laughing about our wood houses that we tear down every 40 or 50 years.
Cheaper to build than brick although there are many brick homes.
I was thinking that too! all the houses here are brick.